1. Field of the Invention
The present invention relates to a cold-rolled aluminum alloy sheet for forming and a process for producing the same. More particularly, the present invention relates to a cold-rolled aluminum alloy sheet for forming which includes ironing, such as in the production of a drawing and ironing (DI) can, and to a process for producing the same.
2. Description of the Prior Art
When working aluminum, the most commonly used materials are pure aluminum and AA 3004-alloy. Pure aluminum offers excellent workability, but is low in strength. Therefore, AA 3004 alloy having H18 temper or H38 temper, which is satisfactory in both workability and strength, is used more frequently. A cold-rolled AA 3004 alloy sheet having H18 temper or H38 temper has a yield strength .sigma..sub.0.2 of from 26 to 30 kg/mm.sup.2 and a tensile strength .sigma..sub.B of from 29 to 31 kg/mm.sup.2 with a cold-rolled degree of from 80% to 90%. If an attempt is made to enhance the rolling degree to more than 90% so as to further enhance the strength, the plastic deformation of the alloy is considerably lowered and the cold rolling becomes difficult.
A known aluminum alloy having a high magnesium content, such as stipulated in Japan Industrial Standard (JIS) 5056, has high strength and excellent corrosion resistance but rather poor formability. High strength heat-treatable aluminum alloys, such as duralmin, super-duralmin, and extra super duralmin, all have high strength, the strength of extra super duralmin being the highest, but have poor corrosion resistance. In addition, although duralmin has good formability, the formability of super duralmin and extra super duralmin is poor.
The term "formability" used herein indicates the cold-working formability required by an aluminum alloy to be cold rolled into a sheet having as small a thickness as possible to produce a thin wall can and indicates the formability or shaping, such as drawing and ironing, required to shape a cold-rolled aluminum-alloy for forming (hereinafter simply referred to as a cold-rolled sheet for forming) into a can.
From the point of view of reducing the amount of aluminum alloys used, and thus saving natural resources, it is necessary to provide a can with a thin wall. In order for such a thin-wall can to have satisfactory strength, the aluminum alloy must therefore have high strength. Such formability and high strength have not been simultaneously possible with known aluminum alloys. Also, a can must clearly be resistive to corrosion due to its contents and to the ambient air and the like. Therefore, all the three properties, i.e., formability, strength, and corrosion resistance, must be combined in a cold-rolled sheet for forming.
Japanese Unexamined Patent Publication (Kokai) No. 52-105509 discloses a process for producing an aluminum-alloy sheet for drawing containing from 0.3% to 1.5% manganese, from 0.1% to 0.5% silicon, and from 0.3% to 3.0% magnesium. The disclosed process is characterized by successively subjecting the aluminum alloy to hot-rolling, initial cold-rolling at a cold-rolling degree of 60% or more, rapid heating to a temperature of from 500.degree. C. to 600.degree. C. followed by rapid cooling, final cold-rolling at a rolling degree of 10% or more, and finally low-temperature annealing at a temperature of from 100.degree. C. to 250.degree. C. The resultant cold-rolled sheet has an approximately 26 kg/mm.sup.2 yield strength, approximately 3% elongation, approximately 1.5% earing percentage, and approximately 1.70 limiting drawing ratio (LDR).